1. Field of the Invention
The present invention is directed to an aerodynamic hood lift deflection measuring device, which is used to measure deflection of a vehicle hood in a wind tunnel.
2. Description of the Related Art
With the increase in gasoline prices, the interest in creating more fuel efficient vehicles has risen dramatically. Among the innovations used to increase fuel efficiency, designers have sought to reduce the weight of vehicles by using lower weight vehicle parts. Of particular interest in the present application is the use of lower weight vehicle hoods.
The vehicle hood (hereinafter, “hood”) may be reduced in weight by either redesigning the underlying structure or changing the material. However, in altering the hood to reduce weight, the hood must still conform with aerodynamic deflection standards and safety requirements. To test the hood lift or deflection, aerodynamic loads are applied to the hood by placing the vehicle in a full-scale wind tunnel and directing an airflow of 160 km/hr over the vehicle. During application of the airflow, the hood lift or deflection is measured.
The measurement of the hood deflection is performed using a laser measurement device. Ideally, the measurement device would be placed underneath the hood in the engine compartment so as to eliminate an aerodynamic footprint of the measurement device. However, space limitations in the engine compartment preclude this location for the measurement device. Therefore, the measurement device is mounted on the exterior of the vehicle, and conventionally on a front fender of the vehicle.
With reference to FIGS. 1A-1D, a conventional measurement device 10 is shown to include a base plate 12, a support leg 14, an arrow-shaped body 16, and a laser device 18. The base plate 12 is secured to a vehicle front fender 20 (hereinafter, “fender”). The fender 20 has a sloped shape extending from a side of a hood 22 and curving downward toward the ground. To ensure a proper attachment, the base plate 12 is similarly curved so as to follow the contour of the front fender 20. The base plate 12 is ideally secured to the fender 20 using an adhesive, though mechanical fasteners or welding can be used.
The support leg 14 extends vertically upward from a hood-adjacent edge of the base plate 12. The support leg 14 is a generally rectangular member that connects the base plate 12 to the arrow-shaped body 16. To ensure stability of the measurement device 10 during testing, the base plate 12, the support leg 14, and the arrow-shaped body 16 are integrally formed as a unitary body, ideally made from aluminum or steel. Alternatively, the measurement device can be formed of a hard polymer.
The arrow-shaped body 16 is disposed at an upper portion of the vertical support leg 14 so as to be vertically spaced from the base plate 12. As shown in FIG. 1D, a top surface of the arrow-shaped body 16 is flush with a top surface of the support leg 14. As the name suggests, when viewed from a top (as in FIG. 1C), the arrow-shaped body 16 has an arrow shape with a relatively narrow rectangular back portion 26 and a triangular front portion 28. A rear wall of the triangular front portion 28 extends laterally from a front wall of the rectangular back portion 26.
An outer sidewall of the narrow rectangular back portion 26 of the arrow-shaped body 16 is integrated with a vertical sidewall of the upper portion of the support leg 14. As such, the arrow-shaped body is disposed over an edge of the hood 22.
The laser device 18 is received within a space defined by an inner sidewall of the rectangular back portion 26 of the arrow-shaped body 16. The laser device 18 has a generally rectangular shaped body shaped and sized to be received within the space provided in the rectangular back portion 26 of the arrow-shaped body 16. The laser device 18 includes an optical opening (not shown) along a bottom surface that is directed toward the vehicle hood 22. A laser beam is directed from the optical opening toward the hood 22 and reflected from the hood 22 back to the laser device 18 so as to measure a distance from the optical opening to the hood 22, as is well known in art of laser measurement.
In this regard, it is noted that since the support leg 14 extends vertically upward from the hood-adjacent edge of the base plate 12, is integrated with the rectangular back portion 26 of the arrow-shaped body 16 along the outer sidewall of the rectangular back portion 26, and the laser device 18 is secured to the inner sidewall of the rectangular back portion 26, the laser device 18 is spaced laterally from the base plate 12 and the fender 20. Therefore, a space between the bottom of the laser device 18 and the hood 22 is unobstructed by the base plate 12.
It is further noted that edges of the base plate 12, the support leg 14, and the rectangular back portion 26 are all substantially parallel with one another. As shown in FIGS. 1A and 1E, when the measurement device 10 is mounted on the vehicle fender 20, the measurement device 10 is pointed in a direction that is substantially parallel with a forward/rearward direction of the vehicle.
While the conventional measurement device 10 is capable of measuring hood deflection upon the application of a sustained air flow, there are several drawbacks to the conventional design. With reference to FIGS. 1E and 6B, the conventional measurement device 10 secured to the front fender 20 is illustrated, with a representative air flow passing over the front fender 20 and the hood 22 with the measurement device 10 secured thereto. FIG. 6A illustrates the air flow over the same region without a measurement device affixed thereto. As is readily ascertained from the air flow pattern following the measurement device 10, the measurement device 10 disrupts the air flow, causing a discontinuation of the air flow upon the air flow contacting the measurement device 10. This discontinuation is illustrated by showing a tail region immediately behind the measurement device 10 as having no airflow passing therethrough. As such, the air flow surrounding this tail region has an increased air flow density.
With reference to FIGS. 8A and 8B, the resultant negative pressure on the hood is shown. FIG. 8A illustrates local negative pressures on the hood when a measurement device is not affixed to the fender. FIG. 8B illustrates local negative pressures on the hood when the conventional measurement device 10 is affixed to the fender. The central region of the local pressure distribution shown in FIG. 8B is the area where the conventional measurement device 10 is located. As shown, the local negative pressure distribution on the hood in the area surrounding the measurement device 10 is greatly disturbed by the presence of the measurement device 10. As such, accurate measurement of the hood lift deflection is not readily ascertainable, as real world conditions are not precisely replicated.
Two features of the conventional measurement device 10 are considered to significantly contribute to the disruption of the air flow. The first is the shape of the measurement device 10. While the arrow-shape does allow the device to somewhat cut through the air flow, the shape is not sufficiently aerodynamic for the present application. The second feature is the positioning of the measurement device relative to the direction of the air flow over the vehicle hood and fender. As illustrated in FIG. 7, the air flow over the edge of the vehicle hood and fender is angled relative to a straight forward/rearward direction of the vehicle. As such, by positioning the conventional measurement device parallel to the straight forward/rearward direction of the vehicle, the device actually interacts with the air flow at an angle. The surface area of the measurement device relative to the air flow is thereby increased, increasing the disruption of the air flow by the measurement device.
Accordingly, there is a need in the art for a hood deflection measurement device that reduces the effect of itself on the air flow, and thereby allows for a more accurate measurement of hood lift or deflection caused by the air flow.